Corrupted Giant Shark

Any creature that starts its turn within 15 feet of the shark must succeed on a DC 17 Wisdom saving throw or take 11 (2d10) Psychic damage.

The shark regains 10 hit points at the start of its turn. If the shark takes Radiant damage or suffers a critical hit, this trait doesn't function at the start of its next turn. The shark dies only if it starts its turn with 0 hit points and doesn't regenerate.

The shark can breathe only underwater.

Melee Weapon Attack +10 to hit (with advantage if the target is a creature missing any hit points), reach 5 ft., one target. 22 (3d10 + 6) Piercing damage, and if the target is a creature, it must succeed on a DC 17 Charisma saving throw or gain 1 level of Exhaustion.